This study will examine mice with bacterial pneumonia of different levels of severity, to determine whether computed tomography scan findings correlate with blood and lung fluid measurements of pneumonia severity. Pneumonia is a major cause of human death and suffering throughout the world. Diagnosis by chest X-ray may not detect pneumonia, particularly early in the course of pneumonia. High-resolution computed tomography scan (HRCT) may increase the ability to detect early pneumonia, and show how severe the course of pneumonia will be. If HRCT imaging can provide better information to predict the severity of pneumonia, then perhaps the intensity of therapy can be matched more closely to the disease severity. Numerous researchers have used mice to compare severity of pneumonia from different strains of microbes, and the body's response to pneumonia, but none have used CT scans to assess pneumonia in mice. Micro-computed tomography (micro CT) is specifically designed for lab animals to be similar to HRCT, and is available in the NIH Mouse Imaging Facility. The use of mice permits study of pneumonia at known times & doses, and the effects of genetic modifiers can be examined using the wide variety of genetically modified mice now available. CT methods pilot-tested in mice have the potential to be quickly translated to human use. [unreadable] [unreadable] This study is being conducted as an initial radiology feasibility study and then 3 parts. The radiology feasibility study is nearly complete: Groups of mice had CT scans in the NIH Mouse Imaging Facility, 24 hours after they received different doses of bacteria[unreadable] injected into their airways to cause pneumonia. These CT scans were scored by 2 independent radiologists. Preliminary statistical analysis indicates a good correlation of scores with the bacterial dose given. The next phases of the study will (I) confirm that lethality of pneumonia at different bacterial doses; (II) characterize the severity of pneumonia at the lethal and non-lethal bacterial doses with well-established measures of pneumonia in bood, lung lavage, and lung tissue samples at 6 hours or 24 hours after bacterial inoculation; (III) confirm that CT scores at 6 hours or 24 hours correlate with blood and tissue measures of the severity of pneumonia.